There are various types of door control systems used to control the doors on mass transit vehicles. Present door control systems are some what exemplified by the systems disclosed in U.S. Pat. No. 4,491,917; U.S. Pat. No. 1,849,516; U.S. Pat. No. 2,096,043; U.S. Pat. No. 3,537,403; U.S. Pat. No. 1,906,699; and U.S. Pat. No. 3,782,034.
A major short coming of the approach utilized in these prior art systems is that the position of the door is sensed using the position of the mechanical linkage that is used to actuate the door. If the door becomes disconnected from its actuating linkage or if the position sensor fails from mechanical wear, the vehicle will be allowed to start even though the door may be in the open condition, or the door may open while the vehicle is in motion and the vehicle will continue to move. Additionally, the present prior art system deactivates the door monitoring control systems after the train or vehicle has begun movement in order to prevent nuisance stopping of the vehicle caused by inadvertent operation of the push back mechanism for the door. People have been killed and injured because doors on transit vehicles have been opened and the vehicle has continued in motion or started in motion. The invention disclosed herein provides a means of detecting the actual physical position of the door independent of the linkage mechanism that actuates the door. The electronic circuitry senses and determines whether the door is closed, pushed back, or opened; and prevents the vehicle from starting its movement if the door is not closed and instantaneously stops the vehicle if the door is opened.
Mechanical wear of switches is a major maintenance problem in the door control systems of transit vehicles. The present invention uses non contacting switches which eliminate this mechanical wear problem.